Dacite pumice (air-fall tephra) from the Holocene of the Philippines.

Mt. Pinatubo is one of several subduction zone stratovolcanoes in the Luzon Volcanic Arc of the Philippines. Published information indicates that Pinatubo is 35,000+ years old and is composed principally of dacitic and andesitic rocks.

Mt. Pinatubo had a significant explosive ash eruption in 1991 that was the largest anywhere on Earth since 1912. Pinatubo's eruption is also famous for having been successfully predicted by American volcanologists. The prediction and subsequent evacuation saved thousands of lives.

The mid-June 1991 eruptions from Pinatubo blanketed ash, pumiceous lapilli, and pumice over the surrounding countryside, including two American military bases (Clark and Subic Bay). The sample seen here is dacite pumice from the 15 June 1991 eruption - it was collected at the U.S. Subic Bay Naval Base, ~20 miles south of Mt. Pinatubo.

Location of volcano: Mt. Pinatubo, Luzon Volcanic Arc, western Luzon Island, northern Philippines

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For additional geologic information on the 1991 Pinatubo eruption, see:

Newhall & Punongbayan (1996) - Fire and Mud, Eruptions and Lahars of Mount Pinatubo, Philippines. Quezon City & Seattle & London. Philippine Institute of Volcanology and Seismology & University of Washington Press. 1126 pp.

Evening twilight over the Lago de Atitlán.

The Lago de Atitlán is a beautiful lake in the highlands of Guatemala; the water level is at 1562 meters (5,125 ft). The lake basin is volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago. It is shaped by deep surrounding escarpments and three stratovolcanoes on its southern flank. Lake Atitlán is the deepest lake in Central America with a maximum depth of about 340 meters (1,120 ft). Its surface area is 130 sq km (50 sq mi).

Mount Zaō (蔵王山, Zaō-san) is a complex volcano on the border between Yamagata Prefecture and Miyagi Prefecture in Japan. It consists of a cluster of stratovolcanoes and is the most active volcano in northern Honshū. The central volcano of the group includes several lava domes and a tuff cone, Goshiki-dake, which contains a crater lake named Okama. Also known as the 'Five Color Pond' (五色沼, goshiki numa) because it changes color depending on the weather, it lies in a crater formed by a volcanic eruption in the 1720s. The lake is 360 metres (1,200 ft) in diameter and 60 m (200 ft) deep, and is one of the main tourist attractions in the area.

en.wikipedia.org/wiki/Mount_Zao

Im sorting out the rest of the picts, this is just a glimpse for you . Unfortunately the weather was awful , so i dont have great pictures :(

From Wikipedia,

Snow covered Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. The volcano is also known as Rucapillán, a Mapuche word meaning "House of the Spirit". It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. Villarrica is one of only a handful of volcanoes worldwide to have an active lava lake within its crater. About 25 scoria cones dot Villarica's flanks. It also has volcanic caves.

The volcano, along with Quetrupillán and the Chilean portion of Lanín, are protected within Villarrica National Park.

Guided hikes to the crater are sometimes offered from the town of Pucón, but may be suspended in periods of seismic or increased volcanic activity. In 2007 a helicopter sightseeing service began to offer flights over the crater.

In the winter (July-September) skiing is practiced on the western slopes of Villarrica.

Elevation :2,847 meters (9,340 feet)

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: Lassen Volcano National Park, northeastern California, USA

This landscape is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The rocky rubble in this photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks, a rock type between dacite and rhyolite. The landslide occurred in the late 1600s A.D., according to carbon-14 dating of trees killed at the time. The Chaos Jumbles Landslide originated from dome C of Chaos Crags, a nearby cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

Only stunted, moderately scattered conifer trees have grown atop the landslide deposit - this is called the "Dwarf Forest".

Locality: Chaos Jumbles, Lassen Volcano National Park, northeastern California, USA

Boat ride from Panajachel to San Pedro La Laguna. In view are the Volcán Tolimán (left) with an altitude of 3158 meters (10,361 ft) and the Volcán Atitlán (right) with an altitude of 3535 meters (11,598 ft).

The Lago de Atitlán is a beautiful lake in the highlands of Guatemala; the water level is at 1562 meters (5,125 ft). The lake basin is volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago. It is shaped by deep surrounding escarpments and three stratovolcanoes on its southern flank. Lake Atitlán is the deepest lake in Central America with a maximum depth of about 340 meters (1,120 ft). Its surface area is 130 sq km (50 sq mi).

ISS021-E-008370 (16 Oct. 2009) --- El Misti volcano in Peru is featured in this image photographed by an Expedition 21 crew member on the International Space Station. The symmetric conical shape of El Misti is typical of a stratovolcano -- a type of volcano characterized by interlayered lavas and products of explosive eruptions, such as ash and pyroclastic flow deposits. Stratovolcanoes are usually located on the continental crust above a subducting tectonic plate. Magma feeding the stratovolcanoes of the Andes Mountains -- including 5,822 meter-high El Misti -- is associated with ongoing subduction of the Nazca Plate beneath the South American Plate. El Misti's most recent -- and relatively minor -- eruption occurred in 1985. The city center of Arequipa, Peru lies only 17 kilometers away from the summit of El Misti; the gray urban area is bordered by green agricultural fields (right). With almost one million residents in 2009, it is the second city of Peru in terms of population. Much of the building stone for Arequipa, known locally as sillar, is quarried from nearby pyroclastic flow deposits that are white in color. Arequipa is known as "the White City" because of the prevalence of this building material. The Chili River extends northeastwards from the city center, and flows through a canyon (left) between El Misti volcano and Nevado Chachani to the north.

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like object at right is a "quenched blob". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Quenched blobs in May 1915 black dacite may be composed of andesite.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. The name of this volcano resembles that of a different volcano, Mount Merapi in central Java, also known as Gunung Merapi; there is also a third volcano named Marapi in Sumatra. The name "Merapi" means "fire" in the Indonesian language.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. The work is low-paid and very onerous. Workers earn around $5.50-$8.30 (Rp 50,000 - Rp 75,000) per day and once out of the crater, still need to carry their loads of sulfur chunks about three kilometers to the nearby Pultuding valley to get paid

(still image from the Brown Peak web camera on Unimak Island, Alaska)

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Shishaldin Volcano is a subduction zone stratovolcano on Unimak Island in the Aleutian Islands of Alaska. Minor lava eruptions in the summit crater started on 12 July 2023. Thirteen episodes of subsequent explosive ash eruptions took place on 14 July, 15 July, 18 July, 22-23 July, 25-26 July, 4 August, 14-15 August, 25 August, 5 September, 15 September, 24 to 25 September, 3 October, and 2-3 November 2023. Seen here is Shishaldin with a prominent white steam plume on 9 November 2023. The Alaska Volcano Observatory reported low-level activity at Shishaldin during the previous day that consisted of small explosive eruptions, volcanic tremor, small earthquakes, a steam plume emanating from the summit area, and an SO2 gas plume.

The Aleutian Arc is a subduction zone formed as the Pacific Plate dives underneath the North American Plate (this area is sometimes called the Bering Plate). The diving plate in subduction zones releases water at depth, which causes partial melting of overlying mantle rocks. The low-density melt rises and eventually reaches the surface, forming volcanoes. All subduction zones have volcanoes and frequent seismicity. Volcanoes in such settings tend to have explosive ash eruptions. Rocks and tephra deposits at subduction zone volcanoes are usually intermediate in composition - typically andesitic to dacitic. Shishaldin's erupted materials in 2023 have been mafic (basaltic).

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Info. at:

en.wikipedia.org/wiki/Mount_Shishaldin

and

en.wikipedia.org/wiki/Aleutian_Arc

Triumph or desaster. You can see so many things in this beautiful photo, which was taken on Tenerife on a walk to the top of the heighest summet in Spain, namely "El Teide" - The sleeping volcano. A more thorough explanation about the Teide can be found underneath:

Mount Teide or, in Spanish, El Teide, is the highest elevation of Spain and the islands of the Atlantic (it is the third largest volcano in the world from its base). It is an active volcano which last erupted in 1909 from the El Chinyero vent on the Santiago (northwestern) rift and is located on Tenerife, Canary Islands. The volcano and its surroundings comprise the Teide National Park (Parque Nacional del Teide in Spanish). The park has an area of 18900 hectares and was named a World Heritage Site by UNESCO on June 29, 2007. It is also from the end of 2007 one of the Twelve Treasures of Spain. Territorially belongs to the municipality of La Orotava. El Teide was a mythological mountain with Aboriginal reministencias Guanches, like Mount Olympus to the ancient greeks. El Teide, the island of Tenerife was in 2008 the most visited National Park of four at their disposal the Canary Islands with a total of 2.8 million visitors, according to the Instituto Canario de Estadística (ISTAC).

At 3718 m above sea level, and approximately 7500 m above the floor of the Atlantic Ocean, Teide is the highest mountain in Spain, highest point in the Atlantic Ocean and the 13th highest mountain in the European Union (highest mountain not in the Alps). (Note: The actual summit stands 3 metres (10 ft) higher than the triangulation station, and associated bench mark, which has an altitude of 3,715 m (12,188 ft)). The island of Tenerife itself is the third largest volcanic ocean island on Earth by volume. Teide is also the third highest volcano on a volcanic ocean island. It is also unstable and possibly in a more advanced stage of deformation and failure than the much publicised Cumbre Vieja. The United Nations Committee for Disaster Mitigation designated Teide as a Decade Volcano, because of its history of destructive eruptions and its proximity to several large towns, of which the closest are Garachico, Icod de los Vinos and Puerto de la Cruz.

Teide together with its neighbour Pico Viejo and Montaña Blanca form the Central Volcanic Complex.

According to legend, Guayota (devil) abducted Magec (god of light and the sun), and took him inside the Teide. The Guanches Achamán asked for clemency to their supreme god. Achamán hit Guayota, Magec was lifted from the bowels of Echeyde and plugged the crater with Guayota in it.

Since then Guayota remains locked inside the Teide. When entering the Teide erupting, it was customary that the Guanches lit bonfires to scare a Guayota.

A Guayota is often represented as a black dog, accompanied by his host of demons Tibicenas.

El Pico del Teide (The Peak of Teide) is the modern Spanish name attributed to the volcano. The Lunar mountain, Mons Pico, part of the Montes Teneriffe mountain range, situated in the inner ring of the lunar mare Imbrium, was named after this 18th Century version by Johann Schröter. Prior to the 1495 Spanish colonization of Tenerife, the native Guanches referred to the volcano as Echeyde. Echeyde, in the Guanches legends, meant some sort of powerful figure leaving the volcano that could turn into hell. The Guanches believed that Echeyde held up the sky.[citation needed] The many "hiding" found in the mountains with archaeological remains of stone tools and pottery have been interpreted as deposits rituals to counter the influence of evil spirits (evil genius), a practice also included in the Kabylia Amazighe. The Guanches conceived the mountain as the place that housed the forces of evil, mostly evil figure Guayota.

The stratovolcanoes Teide and Pico Viejo are the most recent centres of activity on the volcanic island of Tenerife. Tenerife is the largest (2058 km2) and highest (3718 m) island in the Canaries and has a complex volcanic history. The formation of the island and development of the current Teide volcano can be summarised into five stages, as shown in the diagram to the right.

Similar to the other Canary Islands, and Volcanic Ocean Islands in general, the island of Tenerife was built by accretion of three large shield volcanoes, which developed in a relatively short period of time. This early shield stage volcanism formed the bulk of the emerged part of Tenerife. The shield volcanoes date back to the Miocene and early Pliocene and are preserved in three isolated and deeply eroded massifs: Anaga (to the NE), Teno (to the NW) and Roque del Conde (to the south). Each individual shield was apparently constructed in less than three million years and the entire island in about eight million years.

The initial juvenile stage was followed by a period of 2-3 million years of eruptive quiescence and erosion. This cessation of activity is typical of the Canaries, for example La Gomera is currently in this erosional stage. After this period of quiescence the volcanic activity became concentrated within two large edifices; the central volcano of Las Cañadas and the Anaga massif. The Las Cañadas volcano developed over the Miocene shield volcanoes and may have reached 40 km in diameter and a height of 4500 m.

Around 160-220 thousand years ago the summit of the Las Cañadas I volcano collapsed creating the Las Cañadas (Ucanca) caldera. Later a fresh stratovolcano - Las Cañadas II volcano reformed and underwent catastrophic collapse. Detailed mapping indicates that the site of this volcano was in the vicinity of Guajara. The Las Cañadas III volcano formed in the Diego Hernandez sector of the caldera. Detailed mapping indicates that all the Las Cañadas volcanoes attained a maximum altitude similar to that of Teide - which is also referred to as the Las Cañadas IV volcano

Two theories on the formation of the 16 x 9 km caldera exist.

The first is that the depression is the result of a vertical collapse of the volcano. The collapse being triggered by the emptying of shallow (at or about sea level) magma chambers under the Las Cañadas volcano after large-volume explosive eruptions.

The second theory is that the caldera was formed by a series of lateral gravitational collapses, similar to those described in Hawaii. Evidence for the later theory has been found in both onshore observations and marine geology studies

The most recent activity on the island is the NW and NE rifts and the Pico Teide/Viejo stratovolcanoes, erupted material from which partially fill the Las Cañadas caldera. The rifts can be seen as prominent ridges running NE and NW through the island from the Las Cañadas caldera. The rifts are also believed to have built the previous Las Cañadas volcano, and had a part in its collapse. Since the collapse, eruptives from the rifts have filled the resulting embayment with increasingly differentiated lavas and finally developed the Teide and Pico Viejo stratovolcanoes, nested in the embayment itself.

Teide is currently dormant, the last eruption occurred in 1909 from the El Chinyero vent. Historical volcanic activity on the island is associated with vents on the Santiago or NW rift (Boca Gangrejo 1492, Montañas Negras 1706, Narices del Teide or Chahorra 1798 and El Chiyero 1909) and the Cordillera Dorsal or NE rift (Siete Fuentes and Fasnia in 1704 and 1705). The 1706 eruption from the Montañas Negras vent on the Santiago vent destroyed the town and principal port of Garachico, plus several smaller villages.

Historical activity associated with the Montaña Teide - Pico Viejo stratovolcanoes occurred in 1798 from the Narices del Teide on the western flank of Pico Viejo. Eruptive material from Pico Viejo-Montaña Teide-Montaña Blanca which partially fills the Las Cañadas caldera. The last explosive eruption involving the central volcanic centre was from Montaña Blanca ~2000 BP. The last eruption within the Las Cañadas caldera occurred in 1798 from the Narices del Teide or Chahorra (Teides Nostrils) on the western flank of Pico Viejo (Old Peak - which is actually younger than Teide). The eruption was predominantly strombolian in style and mostly a'a lava was erupted. These lavas are visible alongside the Vilaflor - Chio road.

The explorer Christopher Columbus reported seeing "... A great fire in the Orotava Valley...," as he sailed past the Tenerife on his voyage to discover the New World in 1492. This was interpreted as indicating that he had witnessed an eruption in the Orotava Valley.

Unfortunately radiometric dating of possible lavas disproved the eruption theory. However, radiometric dating indicates that an eruption did occur in 1492 from the Boca Gangrejo vent.

About 150,000 years ago, a much larger explosive eruption occurred, probably of Volcanic Explosivity Index 5. This eruption created the Las Cañadas caldera, a large caldera, at about 2,000 m above sea level. The caldera is ~16 km across east-west and ~9 km north-south. At Guajara, on the south side of the structure, the internal walls rise as almost sheer cliffs from 2,100 m to 2,715 m. The 3,718 m summit of Teide itself, and its sister stratovolcano, Pico Viejo 3,134 m, are both situated in the northern half of the caldera, and are derived from eruptions subsequent to this prehistoric explosion.

Further eruptions are possible at some future unascertainable date, including a risk of pyroclastic flows and surges similar to those that occurred at Mount Pelée, Merapi, Mount Vesuvius, Soufrière Hills, Mount Unzen, etc. During 2003, there was an increase in seismic activity at the volcano. Many volcanoes e.g. Mount St Helens, Soufrière Hills had similar seismic activity prior to becoming active. Such activity is considered as being indicative of magma rising into the edifice.

Teide is considered to be unstable and has a distinctive bulge on its northern flank. This bulge is not believed to be associated with an influx of magma, but the result of a slow northwards collapse of the edifice. Seismic evidence suggests that Teide may be constructed over the headwall scarp of the infilled Icod Valley, a massive landslide valley formed by edifice failure in a similar manner to that of the Güímar and Orotava Valleys. The summit of the volcano has a number of small active fumaroles emitting sulfur dioxide and other gases including low levels of hydrogen sulfide.

The lava flows on the flanks of Teide weather to a very thin, but nutrient and mineral rich soil that supports a diverse amount of plant species. Vascular flora consists of 168 plant species, 33 of which are endemic to Tenerife.

Forests of Canary Island Pine (Pinus canariensis) occur from 1000-2100 m, covering the middle slopes of the volcano, and having an alpine timberline 1000 m lower than that of continental mountains of similar latitude. At higher altitudes, the Las Canadas caldera provides sufficient shelter for more fragile species such as the Canary Island cedar (Juniperus cedrus), and the Canary Island pine (Pinus canariensis) to grow.

The most dominant plant species in the Teide National Park are the Teide white broom (Spartocytisus supranubius), which has a white and pink flower; the Canary Island wallflower (Erysimum scoparium), which has white and violet flowers; and the Teide bugloss (Echium wildpretii), whose red flowers form a pyramid up to 3m in height. The Teide Daisy (Argyranthemum teneriffae) can be found at altitudes close to 3,600m above sea level. The Teide Violet (Viola cheiranthifolia) can be found right up to the summit of the volcano, making it the highest flowering plant in Spain.

These plants are adapted to the tough environmental conditions on the volcano such as high altitude, intense sunlight, extreme temperature variations, and lack of moisture. Adaptations include acquiring semi-spherical forms, acquiring a downy or waxy cover, reducing the exposed leaf area, and having a high flower production. Flowering takes place in the late spring or early summer, in the months of May and June.

The Teide National Park contains a huge range of invertebrate fauna, over 40% of which are endemic species, with 70 species only being found in the National Park. The invertebrate fauna include spiders, beetles, dipterans, hemipterans, and hymenopterae.

In contrast, Teide national park has only a limited variety of vertebrate fauna. Ten species of bird nest in the park. These include the blue chaffinch (Fringilla teydea teydea); Berthelot’s pipit (Anthus berthelotii berthelotii); the wild canary (Serinus canaria); and a species of kestrel (Falco tinnunculus canariensis).

Three endemic reptile species are also found in the park – the Canary Island Lizard (Gallotia galloti galloti), the Canary Island wall gecko (Tarentola delalandii), and the Canary Island skink (Chalcides viridanus viridanus). The only mammals native to the park are bats, the most common species of which is Leisler’s bat (Nycatalus leisleri). Other mammals such as the mouflon, the rabbit, the house mouse, the black rat, the feral cat, and the Algerian Hedgehog have all been introduced to the park.

The volcano and its surroundings, including the whole of the Las Cañadas caldera, are protected in a national park, the Parque Nacional del Teide. Access is by a public road running across the caldera from northeast to southwest. The public bus service TITSA runs a once per day return service to Teide from both Puerto de la Cruz and Playa de las Americas. A parador (hotel) is also within the National Park along with a small chapel. The Teleférico cable car goes from the roadside at 2,356 m most of the way to the summit, reaching 3,555 m. Each car carries 38 passengers (34 in high wind) and takes 8 minutes to reach the summit. In peak season, queues can exceed two hours. Access to the summit itself is restricted; a free permit (obtainable from the Park office in Santa Cruz, Calle Emilio Calzadilla, 5 - 4th floor) is required to climb the last 200 m. Numbers are normally restricted to 150 per day.

Due to the altitude, oxygen levels are lower than at sea level. This can cause people with heart or pulmonary conditions to become light headed, dizzy, develop mountain sickness and in extreme cases unconsciousness. The only treatment is to return to lower altitudes and acclimatise.

en.wikipedia.org/wiki/Teide

See where this picture was taken. [?]

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

This landscape is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The large, gray feature in the background is Chaos Crags, a cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. All six domes are composed of porphyritic rhyodacite, a lava type between dacite and rhyolite. Published analyses indicate that the Chaos Crags rhyodacite domes are 68% to 70% silica. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

The rubble in the bottom foreground of the photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks. The landslide occurred in the late 1600s A.D., according to carbon-14 dating of trees killed at the time. The Chaos Jumbles Landslide originated from dome C of Chaos Crags. Dome C is the large front face at the upper right in this picture. Dome C rocks and Chaos Jumbles Landslides rocks are composed of 68% silica porphyritic rhyodacite with ~10 volume% mafic inclusions. Phenocrysts in the rocks are principally plagioclase feldspar, hornblende amphibole, biotite mica, and quartz.

Dome E is the rocky feature at the center-top. It is also composed of 68% silica porphyritic rhyodacite.

Only stunted, moderately scattered conifer trees have grown atop the landslide deposit - this is called the "Dwarf Forest".

Locality: Chaos Jumbles, Lassen Volcano National Park, northeastern California, USA

This landscape is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Mt. Lassen is in the far background on the right side of this photo. The large, gray feature in the center background is Chaos Crags, a cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. All six domes are composed of porphyritic rhyodacite, a lava type between dacite and rhyolite. Published analyses indicate that the Chaos Crags rhyodacite domes are 68% to 70% silica. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

The rubble in the bottom foreground of the photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks. The landslide occurred in the late 1600s A.D., according to carbon-14 dating of trees killed at the time. The Chaos Jumbles Landslide originated from dome C of Chaos Crags. Dome C is the central front face of Chaos Crags, as seen in this picture. Dome C rocks and Chaos Jumbles Landslides rocks are composed of 68% silica porphyritic rhyodacite with ~10 volume% mafic inclusions. Phenocrysts in the rocks are principally plagioclase feldspar, hornblende amphibole, biotite mica, and quartz.

Only stunted, moderately scattered conifer trees have grown atop the landslide deposit - this is called the "Dwarf Forest".

Locality: Chaos Jumbles, Lassen Volcano National Park, northeastern California, USA

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite that formed in 1915.

This boulder is 27 ka pinkish-reddish porphyritic dacite. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like objects are "quenched blobs". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

Granodiorite in the Cretaceous of California, USA.

Moro Rock is a large exfoliation dome in the Sierra Nevada Mountains of eastern California, USA. It is accessible by road and hiking trail in the western part of Sequoia National Park, a little east of Generals Highway (Rt. 198).

Exfoliation domes are common in the Sierra Nevada Mountains. They form by large-scale spheroidal weathering of granites and granitoids of the Sierra Nevada Batholith. The batholith represents a Late Jurassic to Late Cretaceous-aged mass of cooled magma chambers originally beneath a chain of subduction zone stratovolcanoes.

Pressure release from erosional unroofing of the batholith resulted in the rocks having curved sheeting joints. Spheroidal weathering followed, akin to peeling the layers from an onion (“exfoliation”). The end result is a rounded mountain top - an exfoliation dome.

Moro Rock is the type locality of the Cretaceous-aged Giant Forest Granodiorite, one of numerous specific igneous intrusions in the Sierra Nevada Batholith. Granodiorite is dominated by quartz and sodic plagioclase feldspar and some potassium feldspar. The Giant Forest Pluton is also rich in hornblende amphibole (= black crystals) and relatively rich in small, ~honey-colored crystals of titanite (a.k.a. sphene - CaTiSiO5).

Geologic unit & age: Giant Forest Granodiorite, Sequoia Intrusive Suite, late Albian Stage to early Cenomanian Stage, mid-Cretaceous, 97-102 Ma

(looking ~northeast)

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At left is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago. The peak at right is Brokeoff Mountain, which represents part of the western edge of the Brokeoff Caldera.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: view from road southwest of Lassen Volcano National Park, northeastern California, USA

The one thing that's certain here is that I took this shot while sticking my head out the passenger-side window of a Chevy Suburban. Exact location: unknown. Direction I'm facing: unknown. What I do recall is that this is the first of three scenes showing the San Juan Mountains. If you know where this locale is, please enlighten me.

Also, note that the position I've put on the geotagging map is very approximate.

One of the main objectives of our circum-Colorado field-course trip was mining localities in the San Juans. As noted in Part 28, economic geology was the great idée fixe of our professors.

At first I was tempted to crop this photo to remove as much of the peripheral blur as possible, but I could not bring myself to cut out a major portion of that lovely cumulus-congestus cloudscape.

I've had the bad habit, which first surfaced in childhood, of taking pictures of mountain ranges and other notable objects the very first time I see them, even if they are barely perceptible. (This shot of the Parthenon, taken one summer previous, is another example of that syndrome.) But I'm pretty sure I was so excited to see the San Juans here I couldn't resist pulling out my trusty Instamatic.

In any event, this image and its companions have inspired me to revisit the geology of the places they show.

It seems remarkable to me now how much geology has changed since I snapped this. At that point the theory of plate tectonics, still in its infancy, had not reached the consciousness or lesson plans of my university instructors. Half a century later, I can wade through an ample literature tying the formation of the San Juans to the magma-generating propensity of the Farallon Plate subducting under western North America.

So at long last I know this. While they seem to be just another picture-postcard-beautiful mountain range in Colorado, the San Juans have a particularly interesting—and violent—origin story. They began as a large cluster of stratovolcanoes that formed in the Oligocene epoch. Eventually almost a score of calderas developed in this volcanic field, including the one produced by the La Garita Supervolcano in one of the most powerful and extensive eruptions recorded in Earth history.

Volcanic activity continued into the Miocene and Pliocene, but the event that probably did much to thrust the range into its present lofty position was the advent of the Rio Grande Rift.

The rift was in turn one particularly dramatic expression of the Basin and Range lithospheric extension that began in this part of the West in the Miocene. As the crust stretched, a succession of uplifted areas (such as these mountains) alternated with down-dropped sections. That said, I should note that the San Juans lie not in the officially designated Basin and Range physiographic province, but in the Southern Rocky Mountains province instead.

In this region there are also imprints of the earlier, compressional phase known as the Laramide Orogeny. For instance, the adjoining San Juan Basin to the south is a structural feature produced during that time, in the late Cretaceous and early Tertiary.

You'll find the other photos and descriptions of this series in my From the Hall of Disjointed Memories album.

Pyritic dacitic lapilli metatuff (pyritic dacitic meta-lapillistone) from the Precambrian of Minnesota, USA (cut surface). (public display, Soudan Underground Mine State Park visitor center, Soudan, Minnesota, USA)

This is a metamorphosed volcanic tuff. Volcanic tuff is a clastic-textured, extrusive igneous rock that forms by explosive volcanic eruptions. The fragments generated by an eruption are deposited by ash fall or ash flow (pyroclastic flow), then buried and lithified. Lapilli are fragments between 2 and 64 mm in size (= granule- and pebble-sized in sediment classification). Fragments smaller than 2 mm are referred to as volcanic ash and volcanic dust (= sand-sized & silt-sized & clay-sized grains in sediment classification). The rock shown above has abundant lapilli-sized fragments, and is thus a lapilli tuff. The composition of the lapilli is dacitic. Dacite is an extrusive igneous rock that is common at subduction zone stratovolcanoes. It is a high-silica intermediate rock or a low-silica felsic rock, depending on which definition of the felsic-intermediate boundary one uses. This specimen has disseminated pyrite (FeS2 - iron sulfide) and has been metamorphosed, as has much of Minnesota's Precambrian rock record, so a full lithologic name is pyritic dacitic lapilli metatuff. The nature and size of the lapilli are still readily apparent in the rock, despite metamorphic alteration.

The lapilli metatuff succession from which this rock derives is closely associated with the famous Soudan Iron-Formation (see: www.flickr.com/photos/jsjgeology/albums/72157652553006284). A description of the lapilli tuff succession is given by Vallowe et al. (2010): "Dirty white to light grey and in areas, sulfide stained, poorly bedded to massive. Fragments locallly consist of light to dark chert and at times small egg shaped concretions. North and east of the Soudan Mine in Section 27, the unit consists of 1 x 3 cm domains of cherty tuff (± sericite) in, and separated by, a coarse anastamosing sericite-chlorite foliation with pyrite clots common. May have local massive beds nor oriented parallel to foliation. Immediately north of the historic workings of the Soudan Mine, the unit is virtually a sericite-quartz schist with foliation wrapping around 2 to 5 m angular to subrounded cherty tuff clasts."

Stratigraphy: "upper sequence" of Vallowe et al. (2010), above the Soudan Iron-Formation & below the Lake Vermilion Formation, Neoarchean, ~2.7 to 2.72 Ga

Locality: undisclosed locality near the Soudan Mine, Soudan Underground Mine State Park, Soudan, northeastern Minnesota, USA

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Site-specific geologic info. synthesized from:

Vallowe et al. (2010) - Surface and subsurface geologic maps of the Soudan Underground Mine State Park, St. Louis County, northeastern Minnesota. Precambrian Research Center Map Series Map-2010-01.

This is the landscape south of Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in northern California's Lassen Volcanic National Park.

Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen (= well off to the right of this photo) is a large volcanic dome that has developed in the remnants of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today.

At the center-top of the photo is Brokeoff Mountain. At upper right is Mt. Diller. These two peaks form part of the western edge of the Brokeoff Caldera. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

Eruptions still occur in this area. Mt. Lassen last experienced eruptive activity in the early 1900s.

Locality: view from (probably) Bumpass Hell Trail, just south of Mt. Lassen, Lassen Volcano National Park, northeastern California, USA

One of the most active volcanoes in Southern Kamchatka. It is formed from four (predominantly basaltic) coalescing stratovolcanoes. The crater contains a powerful geothermal field with numerous fumaroles, boiling mud pools/springs. Care is required when visiting this site (should keep away from the direction of the toxic fumes emanating from the fumaroles and any unstable areas).

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. The name of this volcano resembles that of a different volcano, Mount Merapi in central Java, also known as Gunung Merapi. The name "Merapi" means "fire" in the Indonesian language. From: wiki.

Java is the world's most densely populated island (population: 136 million). It is home to 60% of Indonesia's population. Much of Indonesian history took place on Java; it was the centre of powerful Hindu-Buddhist empires, Islamic sultanates, the core of the colonial Dutch East Indies, and was at the centre of Indonesia's campaign for independence. The island dominates Indonesian social, political and economic life. More information on wikipedia.

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: Lassen Volcano National Park, northeastern California, USA

Dacite pumice (air-fall tephra) from the Holocene of the Philippines.

Mt. Pinatubo is one of several subduction zone stratovolcanoes in the Luzon Volcanic Arc of the Philippines. Published information indicates that Pinatubo is 35,000+ years old and is composed principally of dacitic and andesitic rocks.

Mt. Pinatubo had a significant explosive ash eruption in 1991 that was the largest anywhere on Earth since 1912. Pinatubo's eruption is also famous for having been successfully predicted by American volcanologists. The prediction and subsequent evacuation saved thousands of lives.

The mid-June 1991 eruptions from Pinatubo blanketed ash, pumiceous lapilli, and pumice over the surrounding countryside, including two American military bases (Clark and Subic Bay). The sample seen here is dacite pumice from the 15 June 1991 eruption - it was collected at the U.S. Subic Bay Naval Base, ~20 miles south of Mt. Pinatubo.

Location of volcano: Mt. Pinatubo, Luzon Volcanic Arc, western Luzon Island, northern Philippines

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For additional geologic information on the 1991 Pinatubo eruption, see:

Newhall & Punongbayan (1996) - Fire and Mud, Eruptions and Lahars of Mount Pinatubo, Philippines. Quezon City & Seattle & London. Philippine Institute of Volcanology and Seismology & University of Washington Press. 1126 pp.

This landscape is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Mt. Lassen is in the far background on the right side of this photo. The large, gray feature in the center background is Chaos Crags, a cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. All six domes are composed of porphyritic rhyodacite, a lava type between dacite and rhyolite. Published analyses indicate that the Chaos Crags rhyodacite domes are 68% to 70% silica. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

The rubble in the bottom foreground of the photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks. The landslide occurred in the late 1600s A.D., according to carbon-14 dating of trees killed at the time. The Chaos Jumbles Landslide originated from dome C of Chaos Crags. Dome C is the central front face of Chaos Crags, as seen in this picture. Dome C rocks and Chaos Jumbles Landslides rocks are composed of 68% silica porphyritic rhyodacite with ~10 volume% mafic inclusions. Phenocrysts in the rocks are principally plagioclase feldspar, hornblende amphibole, biotite mica, and quartz.

Only stunted, moderately scattered conifer trees have grown atop the landslide deposit - this is called the "Dwarf Forest".

Locality: Chaos Jumbles, Lassen Volcano National Park, northeastern California, USA

Maly Semyachik (Russian: Малый Семячик) is a stratovolcano located in the eastern part of Kamchatka Peninsula, Russia. It is a compound stratovolcano located in a 10-km-wide caldera within the 15x20 km mid-Pleistocene Stena-Soboliny caldera. Three overlapping stratovolcanoes were constructed sequentially along a NE-SW line, with the youngest cone, Tseno-Semyachik, at the southwest end. A hot, acidic crater lake fills the historically active Troitsky Crater, which formed during a large explosive eruption of Ceno-Semiachik about 400 years ago.

This landscape is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The rocky rubble in this photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks, a rock type between dacite and rhyolite. The landslide occurred in the late 1600s A.D., according to carbon-14 dating of trees killed at the time. The Chaos Jumbles Landslide originated from dome C of Chaos Crags, a nearby cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

Only stunted, moderately scattered conifer trees have grown atop the landslide deposit - this is called the "Dwarf Forest".

Locality: Chaos Jumbles, Lassen Volcano National Park, northeastern California, USA

ViewFinders_Overseas_Outing - Surabaya --> Ijen --> Bromo --> Solo --> Jogjakarta

Ijen:

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.

An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints.

Bromo:

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 metres (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park.

Mount Bromo sits in the middle of a vast plain called the Sand Sea (Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 meters) (Indonesian: Gunung Penanjakan). The best views from Mount Bromo to the Sand Sea below and the surrounding volcanoes are at sunrise. The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.

Solo:

Surakarta is also known by the name "Solo". "Surakarta" is used in formal and official contexts. The city has a similar name with the neighboring district of "Kartasura", where the previous capital of Mataram was located. Variant spelling of Surakarta is found as Soerakarta - and is simply the old spelling prior to the pre 1948's spelling change.

It is approximately 65 km (40 miles) northeast of Yogyakarta, and 100 km (60 miles) southeast of Semarang The eastern part of the town is bordered by Bengawan Solo River, the longest river on Java. The river is the inspiration for the song Bengawan Solo, a 1940s composition by Gesang Martohartono which became famous throughout much of Asia.

Jogjakarta:

Yogyakarta is located in south-central Java. It is surrounded by the province of Central Java (Jawa Tengah) and the Indian Ocean in the south.

The population of DIY in 2003 was approximately 3,000,000. The province of Yogyakarta has a total area of 3,185.80 km2. Yogyakarta is the second-smallest area of the provinces in Indonesia, after the Jakarta Capital Region. However it has, along with adjacent areas in Central Java, some of the highest population densities of Java.

(photos by James St. John; photo stitch by Mary Ellen St. John)

--------------------

This is the landscape south of Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in northern California's Lassen Volcanic National Park.

Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen (= well off to the right of this photo) is a large volcanic dome that has developed in the remnants of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today.

In the photo, the highest mountain peak in the left background is Brokeoff Mountain, which forms the western edge of the Brokeoff Caldera. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

Eruptions still occur in this area. Mt. Lassen last experienced eruptive activity in the early 1900s.

Locality: view from near Sulfur Works, just south of Mt. Lassen, Lassen Volcano National Park, northeastern California, USA

This is a volcanic deposit near Mt. Lassen (Lassen Peak) (= uppermost left corner), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The scattered boulders shown here are in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, which formed on 14 May 1915. Other clast types present include dacite pumice and banded andesite-dacite pumice, both of which formed on 22 May 1915.

Locality: Devastated Area, Lassen Volcano National Park, northeastern California, USA

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulders shown here are in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

From park signage:

"After the May 19 avalanche carried hot lava rocks here, the surrounding air temperature rapidly cooled them. As they cooled - from the outside in - some of the rocks fractured inwardly and radially like this one, breaking into pyramid-like shapes. Like a jigsaw puzzle, many of the rock pieces you see here today could easily be reconfigured - solving a hot puzzle of the past."

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: Lassen Volcano National Park, northeastern California, USA

(camera lens cap for scale)

----------------------------------------

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The moderately large, darker-colored, xenolith-like object is a "quenched blob". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Quenched blobs in May 1915 black dacite may be composed of andesite.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

This landscape is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The rocky rubble in this photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks, a rock type between dacite and rhyolite. The landslide occurred in the late 1600s A.D., according to carbon-14 dating of trees killed at the time. The Chaos Jumbles Landslide originated from dome C of Chaos Crags, a nearby cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

Only stunted, moderately scattered conifer trees have grown atop the landslide deposit - this is called the "Dwarf Forest".

Locality: Chaos Jumbles, Lassen Volcano National Park, northeastern California, USA

ViewFinders_Overseas_Outing - Surabaya --> Ijen --> Bromo --> Solo --> Jogjakarta

Ijen:

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.

An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints.

Bromo:

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 metres (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park.

Mount Bromo sits in the middle of a vast plain called the Sand Sea (Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 meters) (Indonesian: Gunung Penanjakan). The best views from Mount Bromo to the Sand Sea below and the surrounding volcanoes are at sunrise. The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.

Solo:

Surakarta is also known by the name "Solo". "Surakarta" is used in formal and official contexts. The city has a similar name with the neighboring district of "Kartasura", where the previous capital of Mataram was located. Variant spelling of Surakarta is found as Soerakarta - and is simply the old spelling prior to the pre 1948's spelling change.

It is approximately 65 km (40 miles) northeast of Yogyakarta, and 100 km (60 miles) southeast of Semarang The eastern part of the town is bordered by Bengawan Solo River, the longest river on Java. The river is the inspiration for the song Bengawan Solo, a 1940s composition by Gesang Martohartono which became famous throughout much of Asia.

Jogjakarta:

Yogyakarta is located in south-central Java. It is surrounded by the province of Central Java (Jawa Tengah) and the Indian Ocean in the south.

The population of DIY in 2003 was approximately 3,000,000. The province of Yogyakarta has a total area of 3,185.80 km2. Yogyakarta is the second-smallest area of the provinces in Indonesia, after the Jakarta Capital Region. However it has, along with adjacent areas in Central Java, some of the highest population densities of Java.

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like objects are "quenched blobs". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Quenched blobs in May 1915 black dacite may be composed of andesite.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: Lassen Volcano National Park, northeastern California, USA

Dacitic lapilli metatuff (dacitic meta-lapillistone) from the Precambrian of Minnesota, USA (cut surface). (public display, Soudan Underground Mine State Park visitor center, Soudan, Minnesota, USA)

This is a metamorphosed volcanic tuff. Volcanic tuff is a clastic-textured, extrusive igneous rock that forms by explosive volcanic eruptions. The fragments generated by an eruption are deposited by ash fall or ash flow (pyroclastic flow), then buried and lithified. Lapilli are fragments between 2 and 64 mm in size (= granule- and pebble-sized in sediment classification). Fragments smaller than 2 mm are referred to as volcanic ash and volcanic dust (= sand-sized & silt-sized & clay-sized grains in sediment classification). The rock shown above has abundant lapilli-sized fragments, and is thus a lapilli tuff. The composition of the lapilli is dacitic. Dacite is an extrusive igneous rock that is common at subduction zone stratovolcanoes. It is a high-silica intermediate rock or a low-silica felsic rock, depending on which definition of the felsic-intermediate boundary one uses. This rock has been metamorphosed, as has much of Minnesota's Precambrian rock record, so a full lithologic name is dacitic lapilli metatuff. The nature and size of the lapilli are still readily apparent in the rock, despite metamorphic alteration.

The lapilli metatuff succession from which this rock derives is closely associated with the famous Soudan Iron-Formation (see: www.flickr.com/photos/jsjgeology/albums/72157652553006284). A description of the lapilli tuff succession is given by Vallowe et al. (2010): "Dirty white to light grey and in areas, sulfide stained, poorly bedded to massive. Fragments locallly consist of light to dark chert and at times small egg shaped concretions. North and east of the Soudan Mine in Section 27, the unit consists of 1 x 3 cm domains of cherty tuff (± sericite) in, and separated by, a coarse anastamosing sericite-chlorite foliation with pyrite clots common. May have local massive beds nor oriented parallel to foliation. Immediately north of the historic workings of the Soudan Mine, the unit is virtually a sericite-quartz schist with foliation wrapping around 2 to 5 m angular to subrounded cherty tuff clasts."

Stratigraphy: "upper sequence" of Vallowe et al. (2010), above the Soudan Iron-Formation & below the Lake Vermilion Formation, Neoarchean, ~2.7 to 2.72 Ga

Locality: undisclosed locality near the Soudan Mine, Soudan Underground Mine State Park, Soudan, northeastern Minnesota, USA

--------------------

Site-specific geologic info. synthesized from:

Vallowe et al. (2010) - Surface and subsurface geologic maps of the Soudan Underground Mine State Park, St. Louis County, northeastern Minnesota. Precambrian Research Center Map Series Map-2010-01.

Central Java, Indonesia.

[en-route JOG-KUL. Almost dusk. View of Mount Sindoro- Mount Sumbing volcanic complex. Both are active stratovolcanoes.]

The picture was taken from the plane window seat in Central Java ca. 9K m (ca. 30K ft) asl en-route JOG-KUL flight path. The twin Mount Sumbing and Mount Sindoro (a distance further) are two adjacent mountain, as well as having the shape and height are nearly equal. Mount Sumbing height of about 3340 m asl, slightly higher than the Sindoro (3155 m asl). Located in the east side of the city of Winosobo.

Ref.

Google Earth

en.wikipedia.org/wiki/Mount_Sumbing

fotosintesa.com/index.php/landscapes/210-mount-sindoro-an...

Dacitic lapilli metatuff (dacitic meta-lapillistone) from the Precambrian of Minnesota, USA (cut surface). (public display, Soudan Underground Mine State Park visitor center, Soudan, Minnesota, USA)

This is a metamorphosed volcanic tuff. Volcanic tuff is a clastic-textured, extrusive igneous rock that forms by explosive volcanic eruptions. The fragments generated by an eruption are deposited by ash fall or ash flow (pyroclastic flow), then buried and lithified. Lapilli are fragments between 2 and 64 mm in size (= granule- and pebble-sized in sediment classification). Fragments smaller than 2 mm are referred to as volcanic ash and volcanic dust (= sand-sized & silt-sized & clay-sized grains in sediment classification). The rock shown above has abundant lapilli-sized fragments, and is thus a lapilli tuff. The composition of the lapilli is dacitic. Dacite is an extrusive igneous rock that is common at subduction zone stratovolcanoes. It is a high-silica intermediate rock or a low-silica felsic rock, depending on which definition of the felsic-intermediate boundary one uses. This rock has been metamorphosed, as has much of Minnesota's Precambrian rock record, so a full lithologic name is dacitic lapilli metatuff. The nature and size of the lapilli are still readily apparent in the rock, despite metamorphic alteration.

The lapilli metatuff succession from which this rock derives is closely associated with the famous Soudan Iron-Formation (see: www.flickr.com/photos/jsjgeology/albums/72157652553006284). A description of the lapilli tuff succession is given by Vallowe et al. (2010): "Dirty white to light grey and in areas, sulfide stained, poorly bedded to massive. Fragments locallly consist of light to dark chert and at times small egg shaped concretions. North and east of the Soudan Mine in Section 27, the unit consists of 1 x 3 cm domains of cherty tuff (± sericite) in, and separated by, a coarse anastamosing sericite-chlorite foliation with pyrite clots common. May have local massive beds nor oriented parallel to foliation. Immediately north of the historic workings of the Soudan Mine, the unit is virtually a sericite-quartz schist with foliation wrapping around 2 to 5 m angular to subrounded cherty tuff clasts."

Stratigraphy: "upper sequence" of Vallowe et al. (2010), above the Soudan Iron-Formation & below the Lake Vermilion Formation, Neoarchean, ~2.7 to 2.72 Ga

Locality: undisclosed locality near the Soudan Mine, Soudan Underground Mine State Park, Soudan, northeastern Minnesota, USA

--------------------

Site-specific geologic info. synthesized from:

Vallowe et al. (2010) - Surface and subsurface geologic maps of the Soudan Underground Mine State Park, St. Louis County, northeastern Minnesota. Precambrian Research Center Map Series Map-2010-01.

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like object is a "quenched blob". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Quenched blobs in May 1915 black dacite may be composed of andesite.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

Ijen volcano in East Java contains the world's largest acidic volcanic crater lake, called Kawah Ijen, famous for its turquoise color. The active crater measuring 950x600 m is known for its rich sulphur deposits which are being quarried.

The volcano is one of several active stratovolcanoes constructed over the 20 km wide Ijen caldera, the largest caldera in Java.

Eruptions from Ijen are very hazardous because of the risk of the lake draining to form catastrophic lahars. Sulphur mine inside the crater of Ijen near the shore of Kawah Ijen

Background:

The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi stratovolcano, which forms the 2799 m high point of the Ijen complex. Immediately west of Gunung Merapi is the renowned historically active Kawah Ijen volcano, which contains a nearly 1-km-wide, turquoise-colored, acid crater lake. Picturesque Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. Coffee plantations cover much of the Ijen caldera floor, and tourists are drawn to its waterfalls, hot springs, and dramatic volcanic scenery.

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: Lassen Volcano National Park, northeastern California, USA

Black porphyritic glassy dacite from the 1915 eruption of Mt. Lassen in California, USA.

Mt. Lassen is a large volcanic dome in the northern California portion of the Cascade Range, a sublinear chain of stratovolcanoes formed by subduction of the Juan de Fuca Plate underneath the North American Plate. The Cascade Range starts in northern California and extends into Oregon, Washington State, and into British Columbia.

The black rocks shown here are from the 1915 eruption of Mt. Lassen. The rock is black porphyritic glassy dacite. The white spots are plagioclase feldspar phenocrysts. The black groundmass is mostly dacitic glass mixed with microphenocrysts of various minerals.

Locality: Devastated Area, Lassen Volcano National Park, Cascade Range, northeastern California, USA

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. The name of this volcano resembles that of a different volcano, Mount Merapi in central Java, also known as Gunung Merapi; there is also a third volcano named Marapi in Sumatra. The name "Merapi" means "fire" in the Indonesian language.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an east/west-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 metres (1,184 ft), a surface of 0.41 square kilometres (0.16 sq mi). It is 200 metres (660 ft) deep and has a volume of 36 cubic hectometres (29,000 acre·ft).